Field of the Invention
Embodiments of the present invention relate generally to structures and methods for harvesting energy from electromagnetic radiation. More specifically, embodiments relate to systems for harvesting electromagnetic energy from, for example, infrared and near infrared (such as heat) and visible spectrums and capturing Terahertz energy.
Background of the Invention
There is a great need for inexpensive renewable energy in the world. Ironically, there is an abundance of energy available in the form of sunlight and heat. Using such energy to support modern living, however, requires that energy be converted into electrical form. In fact, most electrical energy used today comes from a conversion process involving heat. For example, nuclear, coal, diesel, and natural gas powered electrical generation plants all convert stored forms of energy into electricity. Unfortunately, the conversion processes used in these plants are inefficient, and often produce more heat as waste than is converted into electricity.
In addition to higher efficiency, harvesting sources of heat into usable electrical power is especially desirable at low cost. Conventional turbine-based solutions for generating electricity from heat are expensive. However, such systems have been employed for years, and are now mature. As a result, new technological solutions to convert heat to electrical power must provide sufficient improvement to overcome the status quo of turbine-based systems. Despite the maturity of turbine-based systems, high cost and greater demand for electricity make new technologies that convert heat to electricity more efficiently and at lower cost increasingly attractive. Among the new technologies being studied are thermo photovoltaic (TPV), thermoelectric (TE) and at lower temperatures organic rankine cycle (ORC).
TPV technology faces a number of hurdles in converting heat to electricity. Chief among them is that photovoltaic techniques convert short wave radiation to electricity, not the comparatively long waves of the IR and near IR spectra associated with heat. New micron gap methods to bring this long wave energy to the operating regions of a PV cell still require conversion technology better suited to the influx of long wave radiation and thus are suitable only at the highest temperature sources.
In general, the PV cell band gap favors only energetic photons since lower energy photons do not have the energy to cross the gap. As a result, these photons are absorbed by the PV cell, and cause heat in the cell itself.
Thermoelectric (TE) solutions, to date, have only been able to convert heat to electrical power at low efficiency. As a result, conventional TE solutions have not provided substantial efficiencies in energy conversion. Even so, TE has found application in automotive waste heat recovery, which further evidences the need for alternative heat-to-electric conversion technologies.
Organic Rankine Cycle (ORC) and related technologies harvest waste heat by chaining turbines together with each successive system in the chain using a lower boiling point liquid. ORC system have a number of drawbacks. They are bulky, have large numbers of moving parts, contain chemicals that are undesirable on customer sites and are limited to the properties of the liquids in the system. Ultimately they suffer from limits of conversion time, space, and the diminishing returns of additional systems in a working space.
These and other problems with conventional techniques for harvesting electrical energy from heat require a solution with greater efficiency and lower costs.